Abstract
The effect of brittle coating precracking on the fatigue behavior of a high-activity aluminide-coated single-crystal nickel-base superalloy has been studied using hollow cylindrical specimens at test temperatures of 600 °C, 800 °C, and 1000 °C. Three types of precrack were studied: narrow precracks formed at room temperature, wide precracks formed at room temperature, and narrow precracks formed at elevated temperature. The effect of precracking on fatigue life at 600 °C was found to depend strongly on the type of precrack. No failure was observed for specimens with narrow room-temperature precracks because of crack arrest via an oxidation-induced crack closure mechanism, while the behavior of wide precracks and precracks formed at elevated temperature mirrored the non-precracked behavior. Crack retardation also occurred for narrow room-temperature precracks tested at 800 °C - in this case, fatigue cracks leading to failure initiated in a layer of recrystallized grains on the inside surface of the specimen. A significant reduction in fatigue life at 800 °C relative to non-precracked specimens was observed for wide precracks and elevated temperature precracks. The presence of precracks bypassed the initiation and growth of coating fatigue cracks necessary for failure in non-precracked material. No effect of precracking was observed at 1000 °C.
| Original language | English |
|---|---|
| Pages (from-to) | 363-369 |
| Number of pages | 7 |
| Journal | Metallurgical and Materials Transactions A |
| Volume | 27 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - Feb 1996 |
Keywords
- aluminum alloys
- brittle fracture
- coated materials
- crack initiation
- failure (mechanical)
- Fatigue of materials
- fatigue testing
- fracture mechanics
- intermetallics
- nickel alloys
- oxidation
- single crystals
- aluminide coated single crystal superalloy
- brittle precracking
- crack retardation
- oxidation induced crack closure mechanism
- superalloys